In multiple-energy projection radiographic imaging, a number of images of the same object are acquired that reveal the x-ray transmittance of the object for differing x-ray spectra. The images are acquired sequentially through the use of an x-ray detector. The images can be decomposed to produce material specific images, such as tissue-only and bone-only images.
Radiographic imaging procedures that require multiple exposures, such as dual-energy imaging, acquire multiple images over a period of time, which may include different stages of the cardiac cycle. The different stages of the cardiac cycle are associated with motion of the heart and the arterial vessels. As such, the relative anatomical motion of the heart and the arterial vessels between the acquired images gives rise to artifacts in the reconstructed image. Anatomical motion and the resulting artifacts can be avoided by timing the image acquisition to occur only during a particular stage of the cardiac cycle, for example diastole when heart motion is minimal. This is commonly referred to as “cardiac gating”.
Electro-cardio-graph (ECG) signals have been used as a method of cardiac gating. ECG, however, requires that electrical contact be made to the patient's skin by means of adhesive pads with attached electronic wires. The electrical contacts are normally attached to areas of the chest. The conductive pads are radio-opaque and can occlude diagnostically important areas of the patient's anatomy. The use of ECG for cardiac gating also requires time consuming preparation of the attachment site, uncomfortable removal of the conductive pads, and the expense and inconvenience of disposable contact pads.
Therefore, there is a need to provide a more convenient and efficient method of cardiac gating for dual-energy imaging that will not occlude the x-ray beam.